Transiting and Variable Objects:
A Search Through Galaxy Evolution Explorer Observations

Kenneth Heafield

Mentor Chris Martin

Co-Mentor Mark Seibert

About GALEX

All-sky ultraviolet sky survey satellite

Two channels: Far (1260-1772Å) and Near (1537-2997Å) Ultraviolet

All observations have timing information

Maximum exposure time of about 1700s

Multiple visits to gain additional exposure time

Variable Stars and Asteroids:
Can they be seen?

Can the GALEX project detect variable stars and asteroids?

What do they look like in the ultraviolet?

Are any of them new discoveries?

On what timescales do the objects vary?

Variable stars and asteroids are found.

88 Variable Stars, 5 Asteroids

Variable stars are found with a wide range of ultraviolet color. Several may be newly discovered.

Asteroids are seen in only one band. They are are all known members of the main belt.

Variability timescales range from 100 seconds to 13 hours.

Findings, Methods, and Problems

Examples of the variable objects found

Finding variable objects

Analyzing variable objects

Database of measurements

Problems Encountered

Further Research

Optical Red Versus Blue

Data from Sloan Digital Sky Survey on found stars

Optical red stars seen flaring

Optical blue stars are periodic

A Large Flare

Known variable GJ 3685A

Largest ever observed ultraviolet flare

100s time intervals

M-dwarf type binary system

Optically red

176.919°, 0.256°

Mysterious UV Blue Dots

Six sightings, all in different places

Not in variable catalogs

Existence confirmed by other surveys

Optically red

Similar to GJ 3685A.

Theory: M-dwarf type stars flaring

Good candidates for time slicing.

Periodic Variables

Known RR-Lyrae variable

Frames with low background like 1, 15, and 60 are short exposures.

Named ROTSE1 J143753.84+345924.8

Periodic Variables Over Time

New Periodic Discovery?

Not in SIMBAD catalogs

Acts quite similar to the previous RR-Lyrae star

Blue in optical

164.093°, 57.089°

New Periodic Over Time

Five Asteroids:
Endymion, Johanna, Kallisto, Phaedra, and Stereoskopia

All Found by streak in only one observation

Kallisto's streak is shown at left.

Minor Planet Center used to identify them

All are in the main belt.

Slicing an Asteroid

200s between frames.

Moved 0.0138 arcsec/s.

Small changes in magnitude

Kallisto observed 03/29/2004 13:30 GMT

164.62°, -0.65°

Finding Variable Objects

Identify overlapping observations

Blink images

Disregard reflections and edge effects

Note for analysis

Analyzing Variable Stars:
Measurements

Created 30 million row, 297 column database of GALEX measurements

Call up all measurements and images of an object in seconds

Confirm visual inspection with quantitative data

Further research: Use database to find variables

FUV and NUV values are Magnitudes in AB.

Outside Databases

Sloan Digital Sky Survey (SDSS): Magnitudes in other wavelengths

SIMBAD collection of catalogs to determine known variables

Digital Sky Survey, Multimission Archive at Space Telescope: Verify UV blue dots

Minor Planet Center Checker to determine if asteroids are known and to identify them

Problems Encountered:
Hotspots

Parts of the detector malfunction

Sometimes stars are obscured

Happens in short exposures

Usually easily recognized by eye

Problems Encountered:
Alignment

Images aligned by tracking guide stars

The tracker can fail or track the wrong star.

Sudden movement can cause two copies of each source.

Problems Encountered:
Source Blending

At left is a binary star system possibly containing a variable star.

Green and red ellipses indicate FUV and NUV detections, respectively

Difficult to measure NUV magnitudes of variable

227.958°, 61.859°

Further Research

Using database

Look for variability in an automated fashion

Match with other surveys

Investigate further the found sources

Study flares (particularly M-dwarfs)

Short time scales

Frequency

Distance measurements using RR Lyrae stars

Spectroscopy of variable sources

Rotation periods of asteroids

Summary

Database of GALEX measurements

GALEX can find variable objects

Asteroids can be observed but must be bright

Variability in stars can be flaring or periodicity

Many variable stars are possible new discoveries

2004-10-04T21:52:37